First of all, you have set a date three months from now at which you time you have decided to 'bite the bullet' and lose your virginity. I think it's a mistake for you to live in the future and schedule your loss of sexuality.
It is much better to live in the now and enjoy your boyfriend during each 'now' moment. Let yourself become more and more intimate with him, because it feels right and because it comes naturally, not because you have told yourself that you should.
The key is to take your time and listen to yourself. Do what feels good and right and nothing more. When the time is right for intercourse, you will know and the experience will flow.
As for pain, you shouldn't experience any pain at all. If you are fully aroused and lubricated, all should go smoothly. I know you may be worrying about your hymen tearing, and you may be fearing that you will bleed and feel pain.
For most women, the hymen is largely disintegrated long before the first time they have intercourse. Exercise, riding a bicycle, gynecological examinations, and tampon use makes the hymen disappear all by itself.
If you want to know whether you still have an intact hymen--which is very rare, just try inserting your finger in your vagina. If you feel an obstruction near the entrance, then you still have a hymen! If this is your case, your partner will just have to make sure to penetrate you gently. You may find it easier for him to 'ease in' by using his finger first. In any case, a couple of penile thrusts and any remaining hymen will be a thing of the past.
If you get nothing else from my letter, just remember that you should just enjoy your time together and let your sexuality unfold naturally. So cross New Years eve off your calender. Who knows, you may not want to wait that long!